1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly to a rechargeable battery including a bare cell having an electrode assembly, a can and a cap assembly, and a protective circuit board electrically and mechanically connected to the bare cell.
2. Description of the Prior Art
As generally known in the art, rechargeable batteries are rechargeable and can be made in a compact form with a large capacity for energy storage, and thus have been broadly researched and developed recently. Typical examples of such rechargeable batteries include nickel-hydrogen (Ni—H) batteries, lithium (Li) batteries and lithium-ion (Li-ion) batteries.
In such rechargeable batteries, most bare cells are formed by inserting an electrode assembly composed of a positive electrode, a negative electrode, and a separator into a container formed of a metal such as aluminum or aluminum alloys, closing the container with a cap assembly, injecting an electrolyte into the container, and then sealing the container. Although the container may be formed of iron compounds, a container formed of aluminum or aluminum alloys has an advantage in that it weighs less by virtue of the light weight of aluminum itself. A battery formed of an aluminum container is free of corrosion while used for a long time under a high voltage.
However, a battery, as an energy source, has a great potential to discharge a large amount of energy. In the case of a rechargeable battery, a large amount of energy is stored in a charged state. Also, in order to charge a rechargeable battery, an external energy source is needed to supply the energy to be stored in the battery. When internal short circuit or malfunction of a rechargeable battery occurs during the above described process or state, the energy stored in the battery may be discharged quickly, thereby causing safety problems such as fire, explosion, or the like.
Lithium rechargeable batteries, which are being used increasingly, include lithium having a high activity, and thus have a great potential for fire or explosion when they are defective. In the case of a lithium ion battery, lithium exists not in a metal state but in an ion state, and thus the safety of the battery is higher than a battery using lithium metal. However, negative electrode materials and non-aqueous electrolytes, etc. used in the battery are flammable, and thus there is a great possibility for fire or explosion when the battery is defective.
Accordingly, in general, a rechargeable battery is equipped with various kinds of safety devices for preventing fire or explosion caused by defect of the battery itself in a charged state or during the charge process of the battery. These safety devices are generally connected to a positive terminal and a negative terminal of a bare cell through a conductive structure, such as a lead plate. These safety devices can interrupt the flow of electric current, for example, when a battery is overheated or a battery voltage rapidly changes due to overcharge/overdischarge, etc., thereby preventing dangers such as explosion or ignition of the battery. Typical examples of safety devices coupled with a bare cell include a protective circuit board that can detect abnormal electric current or voltage to interrupt electric current, a Positive Temperature Coefficient (PTC) device operated according to the occurrence of overheating due to abnormal electric current, a bimetal device, etc.
A rechargeable battery having a bare cell coupled with a safety device is contained in a separate casing so that the rechargeable battery has a finished outer appearance. Further, a bare cell and a safety device, such as a protective circuit board, connected to the bare cell are fixed to each other and are encapsulated with plastic molding to fill the gap between the bare cell and the protective circuit board, resulting in a rechargeable battery having a finished appearance.
In general, rechargeable batteries are made from different materials, and are made into various shapes, sizes, etc., depending on their manufacturers and product models. Accordingly, the design of a suitable safety device is also varied according to such factors. Additionally, general manufacturers of rechargeable batteries integrate a bare cell and a protective circuit board, etc., into one body. In most cases, the compositional material and design are predetermined because the rechargeable battery forms a part of a product set to which it is mounted. Therefore, even if a rechargeable battery has the same operating conditions and functions in the same way as another battery meant for the exclusive use in a desired product set, it is not possible to use the rechargeable battery in the product.
Under these circumstances, rechargeable batteries have no interchangeability among various products, and thus it is difficult for consumers to optionally select a rechargeable battery for use in a desired product.
To solve this problem, a rechargeable battery that can be used in various products has been developed. In order to accomplish this, a rechargeable battery is often made as a pack-type battery, in which the terminals of a bare cell and those of a safety device such as a protective circuit board are bonded by welding, and the space between the bare cell and the protective circuit board is filled with a plastic molding, thereby bonding the bare cell with the protective circuit in a physical manner.
FIG. 1 is a schematic exploded perspective view showing a conventional pack-type lithium-ion battery, before coupling with a plastic molding. FIG. 2 is a sectional view showing a conventional pack-type lithium ion rechargeable battery, which has been coupled with a plastic molding.
Referring to FIGS. 1 and 2, in a pack-type battery, a protective circuit board 30 is disposed parallel to the surface of a bare cell, on which electrode terminals 130, 111 are disposed. Additionally, as shown in FIG. 2, a gap between the bare cell 100 and the protective circuit board is filled with a plastic molding 20. When the gap is filled with the plastic molding 20, the molding may cover even the outer surface of the protective circuit board. However, external input/output (I/O) terminals 31, 32 must be exposed to the exterior.
The bare cell 100 includes a positive terminal 111 and a negative terminal 130 on the surface facing the protective circuit board 30. The positive terminal 111 may be a cap plate that is formed of aluminum or aluminum alloys, or a nickel-containing metal plate bonded to a cap plate. The negative terminal 130 protrudes from a cap plate 110, and is electrically isolated from the cap plate 110 by a peripheral insulator gasket.
The protective circuit board 30 includes a panel formed of a resin, on which a circuit is disposed, and the external I/O terminals 31, 32 are formed on the outer surface thereof. The protective circuit board 30 has a dimension and a shape that are substantially the same as those of the surface (cap plate 110 surface) of the bare cell 100 facing thereto.
The internal surface of the protective circuit board 30 opposite to the outer surface, on which external terminals 31, 32 are formed, is equipped with a circuit section 35 and connection terminals 36, 37. The circuit section 35 includes, for example, a protective circuit for protecting a battery from overcharge/overdischarge during charge/discharge of the battery. The circuit section 35 and each external I/O terminal 31, 32 are electrically connected to each other by a conductive structure passing through the protective circuit board 30.
Connection leads 41, 42 and an insulating plate 43, etc., are disposed between the bare cell 100 and the protective circuit board 30. The connection leads 41, 42, which are generally formed of nickel, are used for the purpose of making electric connection between the cap plate 110 and each connection terminal 36, 37 of the protective circuit board 30. They may have an “L”-shaped form or a planar structure. In order to make electric connection between each connection lead 41, 42 and each terminal 36, 37, a resistance spot welding method may be used. In the embodiment as shown in FIG. 1, a separate breaker is formed in a connection lead 42 disposed between the protective circuit board and the negative terminal. In this case, the circuit section 35 of the protective circuit board has no breaker. The insulating plate 43 is positioned to electrically insulate the connection lead 42 connected to the negative terminal 130 from the cap plate 110 as a positive terminal.
However, when the bare cell 100 and other battery components including the protective circuit board 30 are incorporated into a pack-type battery using a plastic molding, certain mechanical problems arise. Plastic molding part 20 for securely coupling the battery components including the protective circuit board 30 with the bare cell 100 is made of a material different from that of the bare cell 100 including metallic components, such as the cap plate 110 and the can, and has a small contact area with the bare cell 100, thereby showing a weak bonding strength.
For the purpose of increasing the bonding strength, increasing the size of a connection structure such as a lead plate or formation of a separate reinforcing structure may be considered. For example, an embodiment in which a separate reinforcing structure is welded to a cap plate, with a space partially formed between the reinforcing structure and the bare cell so that the space may be filled with a plastic molding while the plastic molding covers the reinforcing structure may be considered. However, in order to form such a reinforcing structure, additional materials and welding processes are needed.
Additionally, in order to pour and cure a resin for plastic molding between the bare cell and the protective circuit board, a mold is needed and should be removed after use, thereby complicating the manufacturing process. Moreover, there is an additional problem in that when a resin for plastic molding is poured, the resin is not uniformly distributed in the gap between the protective circuit board and the bare cell. Particularly, when using a reinforcing structure with a complicated form, it is very difficult to fill the gap between the protective circuit board and the bare cell uniformly with the resin for plastic molding.
In addition, when resin is poured into the gap between the bare cell and the protective circuit board so as to form the plastic molding, the connection parts of terminals, protective circuit board, PTC, etc., are embedded in the plastic molding together, and thus it is not possible to separate them individually. Therefore, when the bare cell is discarded, a safety device attached thereto should also be discarded.